Low tension spark plug



w. A. BYcHlNsKY Low TENSION 'SPARK PLUG Feb. 17, 1959 Filed May 1. 1952 United States PatentO F LW TENSION SPRK PLUG General Motors Corporation, Detroit, Mich., a corpo. ration ofDelawareu research-is -a spark-plug which will-give an-extremely-hotl spark-but which atV the same -time-isdurable and-reliable.- One of the traditional problemsof efficient; spark` plug-- operations `-is the fouling-which-resultsY from-the -fuel addil tives, carbon, oil; etcz, tok which--th'e-plug` issubjected Conventionali type sparle plugs-in common use; today utilize ar relatively large-- sparkgapiny Combination with a'higAh--tension ignition-system: In recent-years; however; ithas beenproposedto use asparkplugA having;i a rel-atvely smallspark' gap iii-combination with-a low-tensioni high energy; ignitionsystem. Bytheg-useoftextremelyhighenergies; a spark canbe'obtainedj despitethe-'fouling'y which'rmight occur; also, because-the spark is hotter thanusual, lowv tension plugs--tendto prevent fouling;

These-low tension spark-plugs-cornprise `apairofelectrodes -electricall'yseparated! by4 aninsulator body; which has-a surface-portion interposed between the ends of-tlieelectrodes-to form a path along the" surface-of theinsulatorI for the formation ofA the discharge.l The insulatormay be formed of-r av semi-conductive material; ror-itsg-sur faceadjacent the-spark gap may-be-coatedfwith a-semiL conductive material. Alternatively, the-insulator surfacemaybe provided with aseries of auxiliary electrodes embedded inthe ceramic in order to-fjorm alow tensionl spark-path: i

Because; however, of: the rapid` electrode erosion; which` occurs; such spark-plugs-have been-foundtohave a relatively-shortlife; This is particularly true when the plugsareused in ahigh' energyignition system whereby-1an extremely hot spark is obtained; It lias-been-,foundl that the; sparkshave `ai tendency to` erodethatv part ofthe-- electrode-which directly abuts the insulator-surface; This; resultslin an enlarged spark gap andi culminates iii-plug failure.-

This invention has as itsl object the provisionoff alow tension spark plug operable athigh energies to-give' an extremely. hot spark and havingv increaseddurability and reliability.

Another object of-the invention is the, provision= ofa low tension sparkplug Which is operable4 at' high energies: and.` which' avoids; rapid electrodei erosion;

It' is impossible, by.- anycommercially-feasible spark.

plug manufacturing: technique, to.. attain.- absolutely* at'.

during; the manufacture-andassembly of-g the; spark-plug;`

parts, there-arebound to occur small gaps, perhaps'u'ndetectably small, between the insulator and* theelectrodes:

I-Lhave-found that `excessive elect-rode erosion is-,causedby--thesparks which form in,v thesenormally occurringgv small gaps between the-insulator surface and-ithe surfacesofV the electrodes. Even where there is but one s uch small gap, and there usually-'willbe a plurality-there is spark-occurrence-wliich -tendsI to enlarge the gap. Grad-v uallv-theelectrodes areundermined andare eroded tothe extent* that they-are out-of contact with the insulator surface. In this way the low tension spark path is eventually destroyed andspark; plug failure-results:

The objects of this ,invention areattained by the-provi sionofgaskets interposed between theY normally insulator; abuttingportions oitheelectrodeandthe insulator in-r ord'er to attain complete andy continuous-- electrical andi mechanical* contact therebetween and: thus preventthe formation of the sparks between the insulatorand eitherof the respective-electrodes. The resultingstructure precludes-j electrode undermining and rapid erosion, thus greatly-increasing the life of the spark-plugs.

ures- 2 and '.-lA show-cross-sectional views-of' other embodi-l rnents-of-the-invention; and Figure-4 shows a side viewv with parts broken away-of still the-invention;

` Referringpnow-to the drawing, )Figurev l; shows -,aspark plugv having an-outer` metal shell 6a`n insulator 8, and-a` center electrode or -centerwire 10 positionedin-the-longitudinally-eXten-ding centerbore 12 ofthe insulator 8i The center-electrode l0 comprises a centerwire screw-l 14-, an electrical conducting seal 16, anda center electrode spindle 18., The centerwire screw 14 is providedv withan electrical contact Ahead 20- for connection withthe ignition wiring-system anda threaded orA serrated portion; ZZwhich is embedded in the electrical; conducting seal 16'V to` retain the cente'rwirescrew within the bore 1,2;

The conductive seal' 16which; may consist ofl-a--rnixtureofglassandsome conductive material such as copperor nickellpowder, is bonded. to the walls of" the insulator centerbore 1'2, thus providinga gas-tightsealandiisalsov prongszfwhich are b ent outwardly andv over thetop of a metal. electrode retainer ring 28 to secure4 thecenterV electrodeinthe lower end 30 of theinsulato-r centerbore 12,. Itwill` be noted, thatthe lower end 30'. ofthe center bore` is of reduceddiameter, thus providing a, centerbore shoulder- 32 to supportthe, retainer ring 28.

In the embodiment shown in Figure 1 the insulator 8.

is of. one-piece construction and is providedwith anoutwardlyextending` annular shoulder` 3ft-and a cylindricalbase.v portion; :i6-Which terminates in a iiat surface 38.

T hisat: surface; 3,8may beA provided Vwith a4 semi-conducei tivegcoatingf or beotherwise-adapted to furnish a low'. ten-V I Sion spark path.

engine.

Patented Feb. 17, 13,59

Va fourth embodiment-of The outer or ground electrode consists of an inwardly extending annular flange 42 which is secured to the metal shell 6 and which, in the embodiment shown, is integral with the ground shell. The edge of the ground electrode is in continuous spaced relation to the edge of the center electrode head, thus providing a circular spark gap 44.

Besides serving as the ground electrode, the ange 42 also cooperates with a circumferential inwardly turned lip 46 on the top of the shell 6 to retain the insulator m position. A metal washer 48 between the insulator shoulder 34 and the lip 46 serves to seal the structure and also to assure a secure fit.

Interposed between the head 24 of the center electrode spindle 18 and the at base surface 38 of the insulator 8 is an annular gasket 50 of some suitable heat and wearresistant deformable metal such as annealed nickel or nickel alloy. A second annular gasket 52 also of a heat and wear-resistant deformable metal such as annealed nickel or nickel alloy is interposed between the outer electrode 42 and the base surface 38 of the insulator. The gaskets 50 and 52 are concentric, with each other, the edge portions being flush with the edges of the respective electrodes to form an aligned continuation of the spark gap 44.

The gaskets 50 and 52 are pressed tightly into continuous mechanical and electrical contact with the abutting surfaces of the electrodes and of the insulator and thus serve not only to inhibit electrode erosion but also as a gas-tight seal for the assembly.

The precise nature of the creep gap or low tension type igniter is not fully understood. It is believed, however, that the electrical discharge which forms along the insulator surface and which may occur at low voltages ionizes the gas or in some other manner conditions the spark gap to allow sparking at low voltage. The precise mechgnism, whereby the spark plug construction of this invention prevents excessive electrode erosion and undermining, is not fully and completely known; however, it has been found that, by the useof heat resistant metal gaskets interposed between the insulator and the electrode as heretofore described, a greatly improved low tension igniter having a much longer life than those of conventional design may be attained. l

The embodiment shown in Figure 2 is particularly adapted for use in aircraft reciprocating engines and c011- sists of a metal shell 56, a metal insert sleeve 58 in electrical contact with the shell 56, an insulator 60 secured within the sleeve 58, and a center electrode or centerwire 62 within a centerbore 64 of the insulator 60. The centerwire structure is quite similar to that shown in Figure 1 and consists of a centerwire screw 66 which has a threaded portion 68 embedded in a conducting seal 70 and a center electrode spindle 72 having a head 74 at its lower end and a bifurcated top portion embedded in the seal 70. The prongs 76 resulting from the bifurcation are bent outwardly over a retainer ring 78 which rests against a shoulder 80 in the insulator centerbore 64.

A center electrode supporting ring 82 of any suitable electrical insulating material threadedly engages the interior of the metal shell as shown at 84 and maintains the center electrode in a concentric position with the shell.

The sleeve 58 is secured within the shell by means of the inwardly extending annular ange 86 on the base of the shell.

The insulator has a lower portion 88 of enlarged diameter which is positioned in the sleeve and which terminates in a flat surface portion 90 which may be provided with a semi-conductive coating or otherwise adapted to furnish a low tension spark path. Washers 92 and 94,

which are positioned between the sleeve and the shell and between the sleeve and the insulator respectively, assure a secure t and also provide a gas-tight structure'.

The base of the sleeve has inwardly turned ange 96 which serves as the ground electrode and is in spaced relation to the head 74 of the center electrode to provide a circular spark gap 98. Interposed between the fiat bottom surface of the insulator 60 and the head 74 of the electrode and between the surfa'ce 90 and the ground electrode 96 are gaskets 100 and 102 of nickel or some other heat-resistant metal. These gaskets are pressed tightly between their respective abutting surfaces to give a firm and continuous mechanical and electrical contact, thereby sealing the structure and preventing electrode erosion and undermining.

In the embodiment shown by Figure 3, the spark plug outer shell is L-shaped and is vconstructed in two sections 112 and 114 secured together by a welding or brazing at the junction 116. The centerwire 118 is likewise L-shaped and has a soldered or brazed junction shown at 120. The upper centerwire section 122 has a threaded portion 124 which is cemented or otherwise substantially secured in an insulator 126, the insulator 126 being held in the upper section 114 of the spark plug shell by means of a nut 128 which threadedly engages the shell. Metal washers 130 and 132 serve to assure a tight t and seal the assembly. Electrical contact with the ignition lead conductor is of course made through the exposed end 134 of the centerwire.

The lower shell section 112 receives an insulator 136 having a centerbore 138 in which there is located the bottom of the centerwire herein referred to as the center electrode spindle 140. A head 142 and a threaded member 144, which engage a threaded portion 146 on the center electrode, serve to retain the electrode within the insulator bore. The top of the electrode is provided with a blind hole to receive the end of the centerwire which is brazed or soldered in place as shown at 148. A metal sleeve 150, having an externally threaded portion 152, threadedly engages the lower shell section and presses the insulator-center electrode 'assembly toward an inwardly extending ange 154 at the base of the shell. Metal washers 156 and 158 are positioned between the threaded member andthe insulator and between the sleeve and the insulator to provide a tight and secure structure. The insulator has a at base portion which may be provided with a semi-conductive coating or other means for furnishing a low tension spark path. The ange 154,

besides serving as an insulator retaining means, also serves as the ground electrode, it being in spaced relation with the edge of the cylindrical center electrode head 142 to provide an annular spark gap 162.

Positioned between the insulator and the respective electrodes are heat-resistant metal gaskets 164 and 166.

As described in conjunction with the embodiments shown by Figures l and 2, these gaskets are in continuous mechanical and electrical contact with the insulator and with the respective electrodes to form a gas-tight seal and to prevent electrode erosion and undermining. The shell section 112 has an annular groove 113 and the central electrode spindle an annular groove 160. In the process of assembling the spark plug the shell is heated to the plastic stage by passing a heavy electrical current through the shell from top to bottom, at which time a pressure is applied to the two ends of the shell which pressure causes the grooved section 113 to collapse and so exert a pressure on the gaskets 158 and 166 thereby insuring a gas-tight assembly. Similarly, the spindle is heated to collapse the grooved section 160 and thereby exert pressure on the gasket 164, this being done prior to the installation of the insulator-electrode assembly into the shell 112. This process is very useful in accomplishing an extremely tight t between the gaskets and the gasket abutting parts. It will be noted that the shell 6 of the embodiment shown in Figure 1 and the sleeve 58 of the embodiment shown in Figure 2 have similar grooves which, in the process of assembly, are used for this same purpose.

The vplug shown by Figure 3 is designed for use in turbine type engines, a ange 168 being secured to the.

shell for suitable mounting.

atmtaaaf The embodiments? shownby Figures: 2: andfa'serve to illustrate the relativelyr small sized electrical insulators which may befused, muclrlessinsulation'being required because` of.` the. low operating,voltagesirequired Figure 4 shows` the lower. end: of:I another gast.l turbine engine. type!l igniter,. 170. beingthe:v outer?` metal shelliand 172%.heingf` the lower end of thei central:electrodettowhicl acylindrically shaped. electrode. head.` 1714 is tlireadedly securedasshownat 176. The. outer:y shell hasta;` groover 1,1'85 whichxreceives .anannular metal ring180 having; an inwardlyl extendingiiange 182ewhich serves as tlief ground electrode. The, base 18.4` of. thev center; electrode: head.` is of enlarged diameterY and isin spaced relationship with the ground electrode 182l to provide the circular spark gap, 186. An electrical. insulator 188; liavingtA at.. semiconductive coating 190 is positioned between the center electrode and the metal insert ring 180 and is secured by the flanges 182, 192 and 194, metal washers 196 and 198, assuring a tight iit. The coating 190 may be a mixture of ceramic and a conductive `or semi-conductive material such as metal powder, metal oxides, carbon, etc., and may be integral with the insulator 188, the entire ceramic unit being monolithic. It will be noted that the semiconductive coating continues along the vertical sides 200 and 202 of the insulator as well as on the flat base 204. In this embodiment of the invention a second coating of nickel or some other suitable metal is provided over the semi-conductive coating on the vertical sides of the insulator body as shown at 206 and 208 to prevent arcing along those surfaces with resulting undermining and erosion. Nickel or other heat-resistant metal gaskets 210 and 212 are interposed between the base of the insulator and the respective electrodes as described in conjunction with previously discussed embodiments of the invention. The metal coating 206 and 208 may be sprayed onto the insulator or may beapplied by any other suitable means. By using such a metal coating, continuous intimate electrical contact between the surfaces of the insulator and kof the ring 180 is assured. The coatings 206 and 208 may of course continue onto the base of the insulator and thus take the place of the gaskets 210 and 212. One way of accomplishing this is to spray the vertical sides and bottom of the semi-conductor coated insulator with a continuous coating of metal and then machine or cut away the circular gap shown at 214.

It is to be understood that such a nickel or other metal coating on the base of the insulator may be used in place of the gaskets shown by Figures l, 2 and 3 and described heretofore in conjunction therewith. Thus, the term gaskets as used herein is meant to include not only the annular metal members as shown in Figures 1, 2 and 3, but also the metal castings as discussed in conjunction with Figure 4.

It is to be understood that, although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

I claim:

1. A spark plug for use at low voltages and at high energies comprising a generally tubular shaped metal shell, an insulator within said shell having a bore extending longitudinally therethrough and having a base with a mass of semi-conductive material thereon, a center electrode in said bore having a cylindrical head portion exterior of the semi-conductive material on said insulator base, an inwardly extending ground electrode connected to the base of said shell having an annular inner edge portion in spaced relationship to the head portion of said center electrode to form an annular spark gap therewith, a thin annular deformable metal gasket positioned between and pressed into continuous electrical contact with said head portion and said semi-conductive material, and a thin annular deformable metal gasket positioned between; and. pressed into. continuous` electricaltcontafct zwithz saidtground electrode. and. said semi-conductive; materiah.

the. distance between said annular gaskets beingat leastas; great; as.. theu distance between.v said. head, portion and L said ground electrode.

2', A spark, plug for use at low voltagesand` athigh energies comprisinga generally tubular shaped metal shell,

an insulator within said shell having a bore extending longrtndinally' therethrough and having a base with a mass inwardl-yextending' ground' electrode` connected toV the base'ofl saidi shell? having an annularfinner edge; portion 1n spaced relationship to the head portionxof.' saidcent'er-` electrode to form an annular spark gap therewith, a thin annular deformable metal gasket positioned between said head portion and said semi-conductive material, a thin annular deformable metal gasket positioned between said ground electrode and said semi-conductive material, the distance between said first-mentioned and said secondmentioned annular Vgaskets being at least as great as the distance between said head portion and said ground electrode, means on said center electrode cooperative with said insulator to press said first-mentioned gasket tightly into continuous electrical contact with said head portion and said semi-conductive material, and means in said shell also cooperative with said insulator to press said second-mentioned gasket tightly into continuous electrical contact with said ground electrode and said semi-conductive material.

3. A spark plug for use at low voltages and at high energies comprising a generally tubular shaped metal shell, an insulator within said shell having a bore extending longitudinally therethrough and having a base with a mass of semi-conductive material thereon, a center electrode in said bore having a cylindrical head portion exterior of the semi-conductive material on said insulator base, an inwardly extending ground electrode connected to the base of said shell having an upper surface coplanar with the upper surface of the head portion of said center electrode' and an annular inner edge portion in spaced relationship to said head portion to form an annular spark gap therewith, a thin annular deformable metal gasket positioned between said head portion and said semi-con ductive material, a thin annular deformable metal gasket positioned between said ground electrode and said semiconductive material, the distance between said first-mentioned and said second-mentioned annular gaskets being the'same as the distance between said head portion and said ground electrode, means on said center electrode cooperative with said insulator to press said inst-mentioned gasket tightly into continuous electrical contact with said head portion and said semiconductive material, and a metal member within said shell pressing against an upper surface of said insulator to press said second-mentioned gasket tightly into continuous electrical contact with said ground electrode and said semi-conductive material.

4. A spark plug for use at low voltages and at high energies comprising a generally tubular shaped metal shell, an insulator within said shell having a bore extending longitudinally therethrough and having a base with a mass of semi-conductive material thereon, a center electrode in said bore having a cylindrical head portion exterior of the semi-conductive material on said insulator base, an inwardly extending ground electrode connected to the base of said shell having an upper surface coplanar with the upper surface of the head portion of said center electrode and an annular inner edge portion in spaced relationship to said head portion to form an annular spark gap therewith, a thin annular deformable metal gasket positioned between said head portion and said semi-conductive material, a thin annular deformable metal gasket positioned between said ground electrode and said semi- 7 8 conductive material, the distance between said first-mem' References Cited in the file of this patent tioned and said second-mentioned annular gaskets being UNITED STATES PATENTS the same as the distance between said head portion and said ground electrode, means on said center electrode llggg Besbson Jlne 16 1914 cooperativewith said insulator to press said first-men- 5 so Il? tezzana Aec' 1?' tioncd gasket tightly into continuous electrical contact 2'248 41 5 Sclsszvl'd'er'ggl' 8 1941 with said head portion and said semi-conductive material, 2507278 Smits "May 9 1950 an annular deformable metal gasket positioned on an 5271489 Smits 24 1950 upper surface of said insulator, and a metal sleeve secured lo 2,605,754 Smits Aug 5" 1952 to the interior surface of said shell pressing against said 2,684,665 Tognola July 27 1954 third-mentioned gasket on said insulator to thereby press 2,786,153 Tognola MaI- 19' 1957 said second-mentioned gasket tightly into continuous elec- Y trical contact with said ground electrode and said semi- FOREIGN PATENTS conductive material. 15 528,269 France Nov. 9, 1921 

